In a wireless communication environment in which one of the communication units is mobile, the reception of RF (radio frequency) signals often requires the use of diversity techniques to combat the effects of Raleigh fading. Various diversity reception methods have been used to reduce the effect of this fading, including such techniques as switching among antennas prior to discrimination, selection among several receivers, and combining signals from several receivers (e.g., max-ratio combining). However, there are drawbacks to these approaches. The use of pre-discrimination antenna switching in analog systems leads to phase discontinuities when the antennas are switched. This in turn results in "pops" in the recovered audio signal, which is unacceptable to most users. This result is even less tolerable in a digital receiver because it leads to unacceptable loss of information (voice and data). Diversity combining approaches like max-ratio combining may lead to acceptable quality, and often better quality than selection diversity techniques, but these come at the expense of a much more computationally intensive implementation. This typically means more expensive circuitry and higher power consumption, both of which are undesirable in mobile communications.
Selection diversity receivers require less circuitry or computations than diversity combining receivers, but prior art selection diversity approaches still typically rely on separate signal paths, each including all the necessary receiver circuitry from the demodulator forward to the antenna. FIG. I illustrates such a prior art diversity receiver. Receiver 110 receives spatially diverse versions of the same signal at antennas 119 114, 116. These signal versions are processed along different signal paths or branches via RF (radio frequency) front ends 122, 124, 126 and demodulators 142, 144, 146. The received signal strengths (RSSI) of the signal versions on each branch are determined in RSSI detectors 132, 134, 136, and the branch having the greatest RSSI is selected via diversity switch 150 using the RSSI information.
The problem with such a prior art selection diversity receiver is that it requires duplicate circuitry and signal processing constantly running in parallel for each signal path, up through and including demodulation. Only after the separate signal paths have been demodulated is a decision (selection) made about which signal to use for the output. This additional circuitry and computational demand ultimately leads to a more expensive receiver and higher power consumption.
Accordingly, there exists a need for a diversity receiver reducing circuitry and computational requirements, but while still performing diversity reception of high speed signals at an acceptable quality and substantially reducing the effects of fading.